Six people were pronounced dead at the scene of the crash along the main route between Phoenix and Las Vegas.

DOLAN SPRINGS, Ariz. — Investigators looking into a deadly tour bus crash on a highway near the Hoover Dam said it may take up to a month to figure out why the vehicle overturned, killing seven passengers and injuring 10 others.

Arizona Department of Public Safety Sgt. Danny Hannigan said the National Transportation Safety Board was assisting in the investigation of Friday's crash. The bus had been taken to Kingman where investigators will scour it over the next week, department spokesman James Warriner said.

Six people were pronounced dead at the scene and a seventh died at a hospital, said Cmdr. Dean Nyhart of the Public Safety Department.

The passengers were Chinese nationals who had flown from Shanghai to San Francisco and had most recently been in Las Vegas, according to the department. They left Las Vegas early Friday for a trip to the Grand Canyon and were returning when the accident occurred on U.S. 93.

Shanghai's municipal government contacted a U.S. travel agency for help in identifying the victims, the official Xinhua News Agency said Saturday. It said the bus was carrying a driver and 15 people from a 20-member group.

There was no immediate word on the identity of the 17th person on the bus.

The bus was traveling north on the two-lane highway — the main route between Phoenix and Las Vegas — when it veered right, overcorrected, crossed the median and rolled at least once before stopping, Nyhart said.